Last year i been working on a pwm true sine inverter .
More or less by coincidence i saw that my 20 Khz carrier came through a standard iron ringcore crispy and clean .
After a little research i learned this.
For higher frequency's in iron core transformers they developed laminated iron with a certain amount of silicon .
From what i was told metalcores at high frequency's can suffer from metal fatigue .
So if you can get a hold of the datasheet of the core used pay some attention to those figures .
For my experiments the iron core did better then expected .
(although i temporary had to stop the project by lack of time for now its still on the shelf)
I would just give it a go .
Just be carefull eventhough a ironcore usualy runs at a higher T then ferrites you can still saturate them
I found that out with a 500 Watt core and it made me a nice blackspot on my desk